Patellofemoral joint disease is the main cause of anterior knee pain (knee pain). During clinical treatment, it is easily missed or misdiagnosed due to atypical symptoms and lack of effective imaging means. The patellofemoral joint is one of the three joints of the knee, and is a joint composed of the patella and the femoral condyle. Patellofemoral joint misalignment refers to a series of clinical syndromes resulting from disorders of patellofemoral joint alignment caused by various reasons, including: patellar dislocation, patellar habitual subluxation, patellar tilt, and the resulting patellofemoral arthritis or patellofemoral arthropathy and other diseases. 1, what are the clinical manifestations of patellofemoral joint misalignment? Most patients with patellofemoral joint misalignment have a history of patellar instability and pain. History of patellar dislocation. The main symptoms include: sudden knee weakness, weakness, kneeling, and a sense of instability. Knee pain, aggravated by activity, especially obvious when squatting up and down stairs and relieved after rest; joint swelling, effusion and pseudocranial locking may occur in the combined presence of severe degeneration of patellar cartilage. Physical examination can be seen as follows: outward patellar displacement or deformity of the knee; increased Q angle; excessive patellar movement, if pushed outward more than 1/2 of the patella, it indicates a weak medial patellar structure; pressure pain at the posterior edge of the patella or patellofemoral joint gap, pain when sliding inside and outside, positive patellar percussion pain; patellofemoral joint friction sound, positive floating patella sign; patellar activity test, fear test, quadriceps impedance test, squat test can be positive. 2.How to detect patellofemoral joint misalignment? X-ray radiographs: ordinary anterior-posterior radiographs of the knee joint are of little diagnostic value. Lateral radiographs can measure the ratio of the patellar ligament to the length of the patella and determine whether there is a high patella and a low patella. A tangential radiograph of the patellofemoral joint (or patellofemoral axial radiograph, mostly taken with Mechant’s knee flexed at 45 degrees) is the most effective way to observe the presence of patellofemoral malalignment. The type of patellofemoral malalignment can be determined by measuring the indicators of this film, such as the slot angle (SA), the overlap angle (CA), the lateral patellofemoral angle (LPA), the lateral patellar tilt angle, and the patellofemoral external displacement distance (LPD). CT scan: A cross-section of the patella at 15-30° of knee flexion can reveal patellofemoral misalignment that is not easily diagnosed by X-ray radiography. Magnetic resonance imaging (MRI): Highly accurate for the diagnosis of articular cartilage lesions. Bone scan: It can determine whether there is intrapatellar hypertension, which is valuable for choosing the surgical procedure. 3.What is the typology and treatment of patellofemoral joint malalignment? The clinical staging of patellofemoral malalignment should be combined with the degree of cartilage lesion, and Ferguson, an American scholar, divided it into three types: (1) patellar tilt type; (2) patellar subluxation type, and (3) patellar tilt combined with subluxation type. Different treatment methods can be adopted according to the clinical types. Conservative treatment methods include: patellar support band pulling massage, quadriceps training, patellar adhesive bandage fixation, orthotics, non-steroidal anti-inflammatory drugs, joint cavity steroid injection and other methods. Surgical treatment: For non-surgical strictly conservative treatment for 3 months is ineffective or severe patellofemoral joint pain or patellar instability is suitable for surgical treatment. Surgical method options: transarthroscopic surgery versus incisional surgery; proximal alignment surgery and distal alignment surgery, etc. For example, proximal alignment surgery such as arthroscopic patellofemoral lateral support band release, and distal alignment surgery such as tibial tuberosity transposition. It is necessary for the specialist to choose carefully according to the needs of the condition and with the consent of the patient.